US Patent 10304728 Double spacer immersion lithography triple patterning flow and method

A system and method for fabricating metal patterns are described. Multiple mandrels are formed on a first polysilicon layer which is on top of a first oxide layer. Each mandrel uses a second polysilicon on top of a first nitride. A spacer oxide and a spacer nitride are formed on the sidewalls of the mandrels to create double spacers. A second oxide layer is deposited followed by removing layers until the first nitride in the mandrels is reached. Areas are etched based on a selected method of multiple available methods until the first oxide layer is etched providing trenches for the metal patterns. Remaining materials on the first oxide layer are removed followed by metal being deposited in the trenches in the first oxide layer.